Conventional heat exchangers include an exhaust pathway through which the exhaust gas passes, a coolant pathway through which coolant passes, and a bypass pathway that bypasses the exhaust gas according to an operating condition of the engine. When an engine operates at a low speed, the exhaust gas passes through the exhaust pathway. However, when the engine operates at a high speed, the exhaust gas passes through the bypass pathway, which is disposed closer to the coolant pathway than the exhaust pathway. The exhaust gas is cooled by the coolant when passing through the bypass pathway, by transferring the heat from the exhaust gas to the coolant.
However, the “heated coolant” may be used to warm-up an engine, or even the cabin of a vehicle. This is known as exhaust gas heat recovery. More specifically, in exhaust gas heat recovery, heat is removed from the exhaust gases of an engine and transferred elsewhere.
While faster engine warm-up to improve fuel economy and cabin warm-up (especially for hybrid vehicles) may be achieved by adding an exhaust gas heat recovery (EGHR) unit in an exhaust system, known EGHR units tend to be fairly large in size. However, because packaging space (especially in hybrid vehicles) is often at a premium, such EGHR units simply cannot be incorporated into certain vehicles.
Further, internal combustion engines often produce undesirable noise within a vehicle, especially when a high flow rate of exhaust gas is generated. Noise is particularly problematic in hybrid vehicles, as changes in ambient noise are noticeable because engines in hybrid vehicles repeatedly turn on and off.
To address such noise, it is known to utilize exhaust mufflers to reduce engine exhaust noise, as well as smooth exhaust-gas pulsations. The exhaust muffler is a separate device from the EGHR unit and may include a series of fixed expansion or resonance chambers of varying lengths, connected together by pipes. With this configuration, the exhaust noise reduction is achieved by the size and shape for the individual fixed expansion chambers. However, exhaust mufflers also take up valuable packaging room within the vehicle, further limiting design options for various components, such as EGHR units.
An EGHR unit that includes an integral noise attenuation device and minimizes packaging space requirements is needed.